Gene therapy using a virus vector has been developed for the purposes of treating cancer and infection disease as well as congenital genetic disease, and many clinical trials have been conducted. In particular, many attempts for gene therapy using a retrovirus vector or an adenovirus vector have been made.
Examples of a transfer vector used for producing a recombinant retrovirus vector used for integration of a desired gene include pLXSN (Genbank Accession M28248) and pMFG which are derived from the wild-type Moloney murine leukemia virus (MoMLV) wherein viral particle-structural protein genes (gag, pol, env) are removed from the genome. In addition, a further modified vector is used in clinical trials for human.
A recombinant retrovirus vector is produced by transfecting a packaging cell (Psi-Crip, GP+E86, GP+envAm12, PG13, etc.) with a DNA vector in which a desired gene is inserted to induce a virus producer cell, culturing the virus producer cell, and then harvesting a supernatant containing the desired virus vector. Then, a packaging cell may be infected again with the supernatant, and from among the infected cells, a clone of a producer cell that can stably produce a retrovirus vector for expression of the desired gene may be selected. Through such a process, a master cell bank (MCB) and then a working cell bank are prepared, and therefrom a recombinant retrovirus vector for gene therapy is stably produced.
Culture of a retrovirus producer cell is very important for increasing the titer of a virus produced from the retrovirus producer cell. In other words, it is required to examine culture conditions for attaining higher viral titer. Methods of increasing viral titer so far as known involve multiple infection (for example, Non-Patent Literature 1), or addition of sodium butyrate or trichostatin A which is a histone deacetylase inhibitor (for example, Non-Patent Literatures 2 and 3). However, these known methods do not produce remarkable effects.